1. Field of the Invention
The present invention relates to a slide unit moving device provided between an apparatus main body of an image formation apparatus and a slide unit provided to be withdrawable from this apparatus main body, and moving the slide unit relatively to the apparatus main body, and an image formation apparatus including the slide unit moving device.
2. Description of the Related Art
Conventionally, a unit withdrawable from an apparatus main body is provided in such an image formation apparatus as a copying machine, a printer or a facsimile machine forming an image on a sheet. Examples of the unit of this type include a sheet cassette accommodating sheets therein, an image formation unit (such as a transfer unit or a fixing unit) forming an image on each sheet, and a duplex unit re-conveying a sheet having one surface on which an image is formed to the image formation unit. The image formation apparatus having the unit of this type provided to be withdrawable from the apparatus main body often includes a mechanism assisting in a withdrawal operation to improve operability for withdrawing the unit.
For example, there is known an image formation apparatus including a sheet cassette that is automatically pushed out upon user's depression of an operation button, as disclosed in Japanese Patent Application Laid-Open No. 11-310331. This image formation apparatus includes a push spring for a user to protrude the sheet cassette to outside of an apparatus main body. If the user pushes the sheet cassette into an accommodation position of an apparatus main body against an elastic force of the push spring when attaching the sheet cassette, a lock member locks the sheet cassette to the accommodation position. While the sheet cassette is being held at the accommodation position, a sheet is fed from the sheet cassette accommodating sheets therein.
If the user unlocks the lock member operating in cooperation with the operation button by depressing the operation button when withdrawing the sheet cassette, the sheet cassette is automatically pushed out by the push spring. This configuration facilitates withdrawing the sheet cassette.
However, the conventional image formation apparatus has the following problems. With the configuration in which the sheet cassette is automatically pushed out by the elastic force of the push spring, it is required to push the sheet cassette into the apparatus main body against the elastic force of the push spring when the sheet cassette is attached to the apparatus main body. Furthermore, the elastic force of the push spring is set high because of need to push out the sheet cassette from the accommodation position even in a state in which sheets are loaded in the sheet cassette up to a maximum loading capacity.
Due to this, the user is disadvantageously required to push the sheet cassette into the apparatus main body with a high force against the elastic force of the push spring when the sheet cassette is attached to the apparatus main body.
Furthermore, a recent image formation apparatus tends to increase a sheet loading capacity of a sheet cassette so as to improve operability while reducing frequency of feeding sheets to the sheet cassette. This disadvantageously requires a user to use higher force to push in the sheet cassette in which the sheets are loaded up to a maximum loading capacity, further deteriorating the operability.
While the operability of sheet cassette is described as above, a similar problem occurs to a transfer unit or a fixing unit configured to enable a transfer portion transferring a toner image onto a sheet or a fixing member fixing the toner image onto the sheet to be withdrawn from an apparatus main body. That is, as the image formation apparatus is increasingly adapted to color image formation, an image formation unit uses a plurality of photosensitive drums and a fixing member having a large heat capacity. This makes the image formation unit large in size and heavy. Due to this, the same problem of deterioration of operability as that with the sheet cassette occurs to configurations of pushing out these units using push springs.
The present invention provides a slide unit moving device that makes it unnecessary for a user to push a unit automatically pushed out by a push spring into an apparatus main body of an image formation apparatus with a high force, and an image formation apparatus including the slide unit moving device.